1. Technical Field of the Invention
The present invention pertains in general to the selection of cell sites in a cellular telephone network, and more particularly, to a method and apparatus for performing local traffic measurements in a proposed location of a "hot spot" micro-cell.
2. Description of Related Art
As the utilization of a cellular telephone network increases additional capacity must be added to the network to accommodate the increased cellular telephone traffic. One method to increase the capacity of a cellular telephone network is to add additional cells to the network. Two methods are available when adding new cells to an existing cellular telephone network. In both a cellular telephone system having hierarchial capabilities and one that does not, an existing cell-site is subdivided into two or more geographically smaller micro-cells with each micro-cell or micro-cells being assigned a distinct set of radio frequencies for effectuating wireless communication with mobile stations. Mobile stations are then typically served by the cell whose base station transmits the strongest signal as measured by the mobile station.
In a cellular telephone system having hierarchical capabilities new cells may also be added to an existing cellular telephone network using what is referred to as a hierarchical cell structure. In this approach, the current cell is not subdivided into two or more cells, but rather, a new geographically smaller micro-cell is located within the geographical service area of the current serving cell or cells. As in the previous approach, the new micro-cell is assigned a set of radio frequencies for effectuating wireless communication with mobile stations. Unlike the previous approach, however, a mobile station is served by the newly added cell whenever the signal strength of the new cell exceeds a threshold level and not when the signal strength of the new cell is the strongest. Among other concerns, the threshold level typically represents the minimum strength required for reliable communication. This new cell is typically located in a geographical area experiencing a high density of slow moving mobile stations. The micro-cell off-loads cellular telephone traffic from the surrounding macro-cell or macro-cells and thereby increases traffic capacity in the surrounding area.
A problem faced by cellular telephone network providers when adding a new cell, is to identify and verify an appropriate location to create the new cell so as to maximize the number of calls off-loaded to the new cell. To aid in site selection, it is desirable to measure the cellular telephone traffic volume at various proposed cell sites. In a current approach to measuring cellular telephone traffic volume in a Global System for Mobile communications (GSM) cellular telephone network, a dummy base station transmitter called a hot spot beacon is located at the proposed cell site and transmits a dummy broadcast control channel signal. Mobile stations in the surrounding area receive the dummy signal, measure the signal strength, and report the signal strength in their signal strength reports routinely sent to a base station currently servicing the particular mobile station. A processor, located at one of the surrounding base stations, compares the signal strength measurements of the dummy base station and the surrounding base stations to determine the number of mobile stations which measured the signal strength of the dummy base station as stronger than the surrounding base stations. These mobile stations are candidates to be served by the proposed micro-cell and represent the cellular traffic volume which could be off-loaded to a micro-cell in a cellular telephone system without hierarchical capabilities.
Several problems exist with the current methods for measuring cellular telephone traffic volume. First, the current method requires the assignment of a radio frequency for use by the dummy base station. On occasion, a radio frequency may not be available or may require a reassignment of the radio frequencies used by surrounding base stations. Furthermore, the processor which calculates the cellular traffic volume in the current method for measuring cellular telephone traffic volume only intercepts signal strength reports from a single base station. Frequently, there are multiple base stations surrounding the proposed micro-cell site and to obtain the cellular telephone traffic volume, separate measurements must be preformed at each base station.
Therefore, it would be advantageous to devise a method and apparatus for determining cellular telephone traffic volume in a cellular telephone system. Furthermore, it would be advantages to devise a method and apparatus for measuring cellular telephone traffic volume which would not require the assignment of radio frequencies. Still further, it would be advantageous to devices a method and apparatus for measuring from a single location the cellular telephone traffic associated with multiple base stations from a single location.